1. Field of the Invention
This invention relates to a method for sensing etch of distributed Bragg reflector (called DBR below) in a real time, more particularly, relates to a method for searching informations about etch speed and etch stop step by monitoring etching procedure in a wet etching method which is a post-process in the semiconductor device manufacturing process. The invention can be applied to the etching method among various post-process steps after growing thin film in the compound semiconductor device manufacturing procedure, both wet etching and dry etching methods.
2. Description of the Related Art
In the conventional art, the etching time was obtained using the data of the thickness of sample etched and the etching speed measured by etch solution in the wet etching process. However, it needed much time and labor to make database for them since there are many samples and various etch solutions can be used according to samples.
Accordingly, the real time growth measurement method can be applied to the wet etch method, which is well known in the thin film growth step which is pre-process stage in the semiconductor device manufacturing process. In the real time growing measurement method, the growing speed of thin film is controlled by analyzing the periodic shapes of intensity of reflected laser beam which is due to its interference of reflection according to the growing thickness during the films having different indices of refraction are growing on the substrate. If applying this to the wet etching method, the intensity of laser beam reflected according to the thickness of thin film which is disappeared by the etching will have periodic shape by the interference. The invention provides a method of recognizing the etching speed regardless of the etching solution by using this principle.
The thin film is grown through the medium of gas under vacuum condition or in the atmospheric pressure so that there is no limitation in the selection of laser beam. However, the laser should be selected in the wet etching process since the laser must pass through the medium of etching solution and most solutions have some characteristic to shut off special wavelengths. Moreover, there is another problem that the etching speed of region on which laser beam is irradiated is different from that of region on which laser beam is not irradiated.